CLN: Convert last of assert_(x == y) to assertEqual

Work on #6175. Fixes last of vanilla assert_(x == y) conversions in pandas/tests and pandas/*/tests. Tests still pass locally.
CLN: Convert assert_(x != y) to assertNotEqual

Work on #6175. Converts instances in pandas/tests and pandas/*/tests. Tests still pass locally.
Merge pull request #6315 from KTAtkinson/issue_6175

BUG: #6175 Got rid of assert_ statements in test_algos.py
Merge pull request #6308 from bwignall/assert_6175_7

CLN: Convert last of assert_(x == y) to assertEqual
BUG: Regression in join of non_unique_indexes (GH6329)
Merge pull request #6330 from jreback/align

BUG: Regression in join of non_unique_indexes (GH6329)
BUG: Issue with groupby agg with a single function and a a mixed-type frame (GH6337)
Merge pull request #6338 from jreback/agg

BUG: Issue with groupby agg with a single function and a a mixed-type frame (GH6337)
BLD: remove -v from nosetests for shorter output
Merge remote-tracking branch 'upstream/master' into issue_6175